The combination of ultraviolet radiation and oxidant, or the use of ultraviolet radiation alone, is a powerful tool for the removal of organic and microbial contaminants from fluids, particularly water. Both hydrogen peroxide and ozone are suitable oxidants for use in ultraviolet radiation/oxidation systems, but ozone is more economical and therefore more often used.
Ozone alone is a strong oxidizing agent that can react with all oxidizable contaminants in the fluid; however, the rate of oxidation can be enhanced by the simultaneous application of ultraviolet radiation. According to equation 1, ultraviolet radiation accelerates the decay of ozone dissolved in water to the hydroxyl radical (.OH), one of the most powerful oxidants known. ##STR1##
Oxidation of organic contaminants by ultraviolet radiation and ozone ultimately yields non-harmful products consisting of carbon dioxide, water and oxygen according to equation 2. The application of ultraviolet radiation and ozone for control of microbial contamination is also a very efficient process because the cell wall of the microorganism is ruptured, killing the organism. ##STR2##
Known ultraviolet radiation/oxidation systems suffer a serious disadvantage, however. Typically, a germicidal ultraviolet lamp is enclosed in a sleeve which is immersed in the fluid to be treated so that the ultraviolet radiation propagates through the fluid. In prior art systems, these sleeves have been made of quartz, one of the few materials that is transparent to the high energy, short wavelength ultraviolet light that promotes the reactions described above.
Quartz sleeves often require cleaning due to water caused fouling. A film tends to accumulate on the quartz sleeve which decreases transmission of the ultraviolet radiation to the fluid. The frequent mechanical or chemical cleaning which is required to remove the film is extremely inefficient since it requires shutting down the fluid decontamination system and draining the fluid to reach the surfaces needing cleaning. Furthermore, quartz which is subjected to ultraviolet light is solarized, producing a slightly tan color in the quartz, which also reduces transmission. Most importantly, quartz sleeves are fragile and expensive.
Immersion of the quartz sleeve in the fluid to be treated disrupts the straight forward flow of the fluid through the reaction vessel and creates eddies and subcurrents such that all the fluid is not irradiated or exposed to the oxidant to an equal extent. Therefore, the contaminants are inefficiently treated.